1. Field
This invention relates generally, to pressure-suppressing arrangements for nuclear reactor power systems and more particularly, to a missile barrier and radiation shield structure that surrounds the reactor vessel head as part of a containment structure for such plants.
2. Related Art
A reactor containment system of the condenser type, such as described in U.S. Pat. No. 3,423,286, issued Jan. 21, 1969, and assigned to the Assignee of this invention, is designed to rapidly absorb the energy release from the reactor coolant system in the improbable event of a loss of coolant accident. The energy is absorbed by condensing the steam in a low temperature heat sink consisting of a suitable quantity of fusible material in a solid state, such as ice, stored in a completely enclosed generally annular refrigerated compartment located radially between an inner wall which defines a reactor compartment and the outer wall of the nuclear plant containment, at an elevation generally above an operating deck which divides the reactor compartment into a lower compartment and an upper compartment.
In the event of a loss of coolant accident, door panels located at the bottom of the condenser compartment open almost immediately due to the pressure rise in the lower compartment caused by the release of reactor coolant. This allows the steam to flow from the lower compartment into the ice condenser. In turn, door panels at the top of the ice condenser compartment open and allow some of the air which was initially in the lower compartment and the ice condenser compartment to flow into the upper compartment. The ice condenser quickly begins to condense the steam, thus limiting the peak pressure in containment. Ice condenser plants require large missile barriers around the reactor head to funnel released loss of coolant accident energy to the ice condenser and to provide neutron shielding for the upper containment to permit ice condenser maintenance during power operation.
The current designs for the radiation shield and missile barriers are approximately two to four feet (0.61 to 1.22 meters) thick and do not provide the ventilation needed to cool the cavity walls surrounding the vessel head to enable safe personnel access to the reactor interior. It is has been found that the confined space within the barriers leaves the very thick concrete walls at elevated temperatures for many days or weeks as there is limited air circulation to create cooling. In addition, it would be desirable to reduce the “touch time,” that is the time associated with handling the barriers to reduce the radiation exposure of maintenance personnel.
Accordingly, it is an object of the embodiment set forth hereafter to improve the air circulation within the radiation barriers surrounding the reactor vessel head to promote cooling of the concrete walls of the barriers during a reactor shutdown, so that the wall temperatures can be reduced to a safe level for access by maintenance personnel.
In addition, it is an object of the embodiment set forth hereafter to provide an improved barrier design that will lessen the weight of the barrier sections so that they can be more easily handled in a time effective manner to reduce radiation exposure to maintenance personnel.